1. Field of the Invention
This invention relates to organosiloxane lubricant compositions. More particularly, this application relates to lubricant compositions containing a class of heat resistant liquid polydiorganosiloxanes that are uniquely suitable for use as mold release agents and lubricants for textile fibers.
2. Background Information
Because liquid polydiorganosiloxanes have good heat resistance and releasing characteristics, these materials have been widely used as mold-releasing agents during the molding of thermoplastic resins, thermosetting resins, and various rubbers, and as toner releasing agents for electrostatic copying machines. When liquid polydimethylsiloxanes, which are representative of the class of liquid polydiorganosiloxanes, are used as release agents for metal molds, they undergo a gradual thermal decomposition as the mold approaches about 150.degree. C. This decomposition is more drastic at higher temperatures such as above 200.degree. C., producing sticky gel-like materials. Because of this problem, when a liquid polydimethylsiloxane was used as a lubricant for an extended period of time as the mold-release agent, once in a while moldings having smooth surfaces could not be obtained due to accumulation of the gel-like substance. In particular, when the surface of the moldings are required to be as smooth as mirror finished surface, occurrence of the gel-like substance has been the fatal fault.
Also, in the high speed xerographic copiers, the heated roll is used at a high temperatures, typically about 200.degree. C., and when liquid polydimethylsiloxanes are used as the toner releasing agent, their thermal decomposition presents a problem. In order to improve the productivity of molding or to shorten the copying time, the temperatures of the metal mold or the heated roll of the copier have recently tended to be raised even higher. Therefore, there has been a demand for releasing agents having improved heat resistance.
Mold-release agents consisting of a mercapto-functional liquid polydiorganosiloxane with a phenol oxidation inhibitor of specific structure are disclosed in Japanese Laid Open Application (Kokai) 61-218660. Amino group-containing liquid polydiorganosiloxanes with an amine equivalent within a specified range are described in Japanese Laid Open Application (Kokai) 3-227206.
As for the toner releasing agents, liquid polydiorganosiloxanes containing organofunctional groups such as carboxyl groups, hydroxyl groups, amino groups, and epoxy groups are described in Japanese Laid Open Patent Application (Kokai) 51-36141).
Because of their excellent heat resistance, similar types of liquid polydiorganosiloxanes are used as lubricants for various synthetic fibers such as lubricants during false twisting of textile fibers, and as lubricants for carbon fibers and tire cord fibers. Polydiorganosiloxanes used for these applications, such as amino group-containing polydiorganosiloxanes are described in Japanese Laid Open Patent Application (Kokai) 60-185879, 60-185880.
However, when these amino group-containing liquid polydiorganosiloxanes are applied during a heating process at temperatures above 300.degree. C. as practiced in the thermosetting process of textile for the industrial tire cord or in the manufacturing process of carbon fiber, they occasionally emit a characteristic ammonia odor, discolor, or cause gelation during extended heating cycles, and therefore, are not completely satisfactory.
U.S. Pat. No. 5,138,012, which issued on Aug. 11, 1992, describes curable organosiloxane release coating compositions wherein at least one siloxane unit of the curable polyorganosiloxane contains a phenolic radical having from 6 to 25 carbon atoms. One of the carbon atoms on the phenyl ring of the phenolic radical is bonded to silicon by an alkylene radical.
The present inventors have found that certain non-reactive liquid hydroxyphenyl-substituted polydiorganosiloxanes having an average phenol equivalent weight within a specific range exhibit excellent heat resistance, releasing characteristics, and lubricity, and that all of the above-mentioned problems can be solved when these polymers are used in the applications discussed in the preceding paragraphs.
The objective of the present invention is to provide a class of liquid non-curable organosiloxane lubricant compositions exhibiting excellent heat resistance, releasing characteristics, and lubricity.